A string of anti-Semitic rants about Sen. Joe Lieberman have popped up on the liberal MoveOn.org’s open forum Web site, drawing criticism from the Anti-Defamation League.

It’s the latest flap in the contentious race between Lieberman, who is running as an independent to keep his seat in Connecticut, and upstart Ned Lamont, the Democratic nominee.

“We recognize that Action Forum is an open forum intended to foster the free flow of ideas,” ADL head Abraham Foxman said in a letter dated Aug. 31 to MoveOn, which supported Lamont in the Democratic primary against Lieberman.

“Nevertheless, since such profoundly offensive content is appearing on a board clearly linked to MoveOn.org, we believe you should assume some responsibility to respond to this hateful content,” Foxman wrote in the letter, which was forwarded by Lieberman’s campaign.

Foxman cited examples from the site’s Action Forum, including “media owning Jewish pigs,” “Zionazis,” a reference to the senator as “Jew Lieberman” and the question, “Why are the Jews so Jew-y?”

Foxman wrote, “Those who allow hate to rear its ugly head under their auspices bear a special responsibility to distance themselves from that hate, and to speak out against it, as loudly as possible.”

Lieberman is one of the country’s best-known Jewish politicians.

Foxman and Eli Pariser, executive director of the MoveOn Political Action Committee, couldn’t be reached.

But in a statement posted on the MoveOn site Saturday, Pariser condemned the anti-Semitic rants.

“Once in a while – as in any public forum – inappropriate material is posted,” he wrote. “Recently, a few of the thousands of comments that are posted every week contained anti-Semitic language.

“The comments that were posted were abhorrent. We were dismayed to see them, and removed them as soon as they came to our attention 17 days ago.”

He added that most of the comments were not made by MoveOn members and suggested it could be an effort by conservatives to “target” the group, and said any effort to tie the rants to MoveOn was “wrong.”